Process for treating spent hypochlorite solutions



PROCESS FOR TREATING SPENT HYPOCHLORITE SOLUTIONS Thomas D. Chisnall, Southampton, England, assignor. to

Esso Research and Engineering Company, a corporation of Delaware No Drawing.

Serial No. 383,375

2 Claims. (CI. 23-86) Application September-30, 1953,

This invention relates to an improved Chemical treating process particularly adapted for use inthe refining of oleaginous fractions containing deleterious sulphur compounds, for example hydrocarbon fractions derived from or obtained from mineral oils.

The'presence'of elemental and combined sulphur is particularly undesirable in lower boiling mineral oilfractions such-as gasolines and kerosines. The sulphur in the higher boiling fractions is generally in the form of more or less stable'and neutral organic compounds which have no deleterious effect on the oil; generally no effort is made to remove them.

The lower-boiling fractions occasionally, contain elemental sulphur in small proportions which may be removed by special procedures. Hydrogen sulphide is nearly always present and is removed by any simple method of washing the hydrocarbons with an aqueous alkaline reagent such as caustic soda, soda ash and lime.

Cracked naphthas, in particular, nearly always contain small quantities of mercaptans which have an objectionable odour and other undesirable properties. These compounds are commonly transformed by an oxidation procedure known as sweetening into the less odoriferous disulphides which remain in the oil. It is with such a process that this invention is concerned.

The use of hypochlorites for the sweetening of hydrocarbon fractions is well known. Sodium and calcium hypochlorites are the most commonly used although other metal hypochlorites such as aluminium, zinc, manganese, iron or copper may be used.

The action of hypochlorite on sulphur compounds depends on factors such as the type and molecular weight of the sulphur compounds, the degree of free alkalinity of the hypochlorite solution, the amount of available chlorine, the volume ratio of the hypochlorite solution to the naphtha solution, and the time and intensity of agitation. Generally hypochlorite does not attack all the sulphur compounds and there does not normally result an overall desulphurisation of the oil.

Under the mild oxidation mercaptans are converted to disulphides by a mechanism that is believed to be illustrated by the equation:

where R represents an organic radical, e. g., methyl, ethyl or propyl. When the conditions for oxidation are more severe, as with stronger hypochlorite solutions, longer exposure, less alkali, etc., the mercaptans and alkyl disulphides, the latter being the products of the milder oxidation of mercaptans, are converted into the corresponding alkyl sulphonic acids. The simplest equation for this oxidation of the mercaptan is probably:

The sulphonic acids of the lower molecular weight hydrocarbons and their sodium salts are soluble in water and removed from petroleum distillates by washing. The

2,784,057 Patented'Mar.

allkyl sulphides, RzS when energetically oxidised first yield sulphoxides v R2S+NaOCl=RzSO+Nacl and on further oxidation yield sulphones RzS+2NaOCl=RzSO2+2NaCl p v These reactions are purely schematic and are representa-'*' tive of the many and complex reactions that may take place.

It is normal for the hypochlorite solution to be a solu tion of sodium hypochlorite with caustic soda. intact, a particularly effective treatment for sweetening thesolu tion contains substantially more caustic than hypochlorite. Thus, normally less than -50 grams/litre of hypochlorite areused whereas the concentration of caustic may be-as low as'2, 5 or 10 grams/litre but is preferably in excessof "50 grams/litre. It will thus be clear that the spent hypochlorite solution i. e. the solution that has been used for treating a hydrocarbonv stream-contains unexpended sodium hypochlorite, caustic soda, sodiumchlqride and various products of the reaction treatment. '3 This spent hypochlorite solution is useless as it leaves the treatment and yet it contains valuable quantitiesof hypochlorite to render it suitable for addition to therefinery caustic line.

It has now been discovered that the residual hypochlorite in spent hypochlorite solution may be decomposed, the resulting solution will then contain sodium chloride, to give a solution that may be returned to the refinery caustic stream.

The solution may be contacted with steam in a jet mix ing zone and then conducted to a decomposing zone. Under these conditions the decomposition takes rather a long time and it has now been discovered that the process may be considerably accelerated by the addition of ammonia or a compound that yields ammonia with the caustic soda under the conditions of regeneration and reacting this ammonia yielding compound at elevated temperature, e. g. by boiling. It is believed that the overall process may be:

A useful source of ammonia for this process is an ammonium salt such as ammonium chloride, thus:

The benefit of the present invention may be appreciated from the following examples. In these examples an ammonia yielding compound was added to the spent hypochlorite and the mixture was boiled for 30 minutes. Four methods of addition of the ammonia yielding compound-- in this case ammonium chlon'de-were tried, viz.

(1) Solid NH4C1 added to cold hypochlorite and the whole boiled.

(2) Drip feeding solution (0.15 gm. Nl-LzCl per litre) over the entire period of boiling.

(3) Total solution added to boiling hypochlorite instantly and boiling continued.

(4) Solution added over a period of one minute to boiling hypochlorite.

a I Y, 3 The results of these four methods of addition are below:

After 3 hours.

The amount of ammonia or ammonia yielding compound used depends on the rate at which decomposition is required. Aslittle asMt lb. of ammonium chloride per 10 barrels of hypochlorite has some effect but generally the minimum quantity is 1 lb./10 barrels. The upper limit is equally variable; for instance more than 50 lb./ 10 barrels can be used but is economically unjustifiable and leads to undesirable pollution of the refinery line. Genorally from 2 to 20 lb./10 barrels is a preferred range, particularly desirable being the range from 5 to lb./ 10 barrels; In the above table the 2 to 4 grams of ammonium chloride added per liter of hypochlorite is roughly equivalent to 7 to 14 lbs. per 10' barrels of hypochl'orite. I v

' The duration or boiling will obviously depend on the amount of sodium hypochlorite that can be tolerated in the refinery line. It has been found that the addition of 7- lb'. of ammonium chloride per 10 barrels of hypochlogiven rite reduced the time of decomposition to" a tolerable level from 24 hours to 3 hours with consequent saving. of fuel and capacity.

What I claim is:

1. A process for decomposing the hypochlorite in a spent aqueous solution of a metal hypochlorite and an alkali metal hydroxide, which solution has been used for the sweetening of a hydrocarbon distillate, which comprises heating the said solution to boiling, adding ammonium chloride thereto, and continuing the boiling for suiiieient time to effect a substantial conversion of the hypochlorite to the corresponding chloride.

2. Process as defined by claim 1 wherein from 2 to 20 pounds of ammonium chloride are added per 10 barrels of spent hypochlorite solution.

References Cited in the file of this patent UNITED STATES PATENTS 910,858 Raschig Jan. 26, 1909 1,480,166 Joyner Jan. 8, 1924 2,228,295 Yabrofi Ian. 14, 1941 2,550,668 Brandon May 1, 1951 2,608,523 Waddell et al Aug. 26, 1952 2,631,121 Linn Mar. 10, 1953 2,675,298 Weiler et a1 Apr. 13, 1954 FOREIGN PATENTS 139 Great Britain A. D. 1908 OTHER REFERENCES The Chem. of Hydrazine, by Audrieth and Ogg, pp. 29-31, 35, John Wiley and Sons, Inc., N. Y. 

1. A PROCESS FOR DECOMPOSING THE HYPOCHLORITE IN A SPENT AQUEOUS SOLUTION OF A METAL HYPOCHLORITE AND AN ALKALI METAL HYDROXIDE, WHICH SOLUTION HAS BEEN USED FOR THE SWEETENING OF A HYDROCARBON DISTILLATE, WHICH COMPRISES HEATING THE SAID SOLUTION TO BOILING, ADDING AMMONIUM CHLORIDE THERETO, AND CONTINUING THE BOILING FOR SUFFICIENT TIME TO EFFECT A SUBSTANTIAL CONVERSION OF THE HYPOCHLORITE TO THE CORRESPONDING CHLORIDE. 